1. Field of the Invention
The present invention relates to an aqueous epoxy resin composition containing water as the medium. More particularly, it pertains to an aqueous epoxy resin composition that can be utilized in a wide variety of industrial applications such as a coating material used for the purpose of anticorrosion or decoration, an adhesive for civil and building work or the like.
2. Description of Related Art
An epoxy resin is widely utilized in a variety of industrial fields by virtue of a number of excellent characteristics in comparison with the other types of resins in terms of adhesivity to various substrates, heat resistance, chemical resistance, electrical properties and mechanical properties. In recent years it has been particularly active in the field of coating materials.
In general, the types of the epoxy resin compositions that are employed in the field of coating material or adhesive are roughly classified into liquid type without the use of a solvent (solventless type), liquid type by the use of an organic solvent as the principal medium, liquid type by the use of water as the medium and solid type (powder).
Among the aforementioned types, the solventless type epoxy resin composition is used as the composition in which an epoxy resin in the form of liquid at ordinary temperature is lowered in its viscosity by the use of a low-viscosity curing agent and a high boiling diluent. However, it is inevitable that, in the course of producing a low-viscosity curing agent, a large amount of free amines and phenols that are harmful to human beings have to be used, and even in the case of a diluent that is relatively less harmful to human beings, the use of such diluent deteriorates the performance of a curing agent.
The liquid type epoxy resin composition using an organic solvent as the principal medium is used generally by dissolving a high molecular epoxy resin in the form of solid at ordinary temperature by the use of a low-viscosity solvent such as xylene, toluene, cellosolve, ethanol or n-butanol and permits a wide selective range of curing agents. Accordingly, the above-mentioned composition not only affords a high-performance cured product but also permits the arbitrary regulation of the viscosity of the composition, thereby finding a number of applications for the above-mentioned purposes. Nevertheless, the composition suffers the disadvantage including harmfulness to the workers handling such an organic solvent, environmental pollution and possibility of such hazard as fire or explosion.
On the other hand, the solid-type epoxy composition is a combined product of a solid epoxy resin with a solid curing agent. The purpose of use thereof is principally a coating material but is limited with regard to its workability. On the contrary, the aqueous epoxy resin composition is obtained by dispersing or dissolving an epoxy resin and a curing agent in water and forms a composition excellent in workability free from the aforesaid drawback which is inherent in the other types of compositions except for the performance of the cured product therefrom.
It is the present situation, however, that an aqueous epoxy resin composition having satisfactory performance has not yet been developed by reason of a large amount of a surfactant required, unavailability of a proper curing agent and the like. There have certainly been partly put into practical use or suggested aqueous epoxy resin compositions using as a curing agent, an adduct of diethylene triamine to an epoxy compound or an amidoamine obtained by reacting an aliphatic amine such as ethylenetriamine with an aliphatic carboxylic acid. Nevertheless, any of the above-mentioned curing agents is far from overcoming the aforestated disadvantages.
As a result of intensive research and investigations made by the present inventors on the above-described subject, it has been discovered by them that the problem can be solved by dispersing in water a curing agent comprising an epoxy resin and a specific amidoamine. The present invention has been accomplished on the basis of the foregoing finding.